The present invention relates to a linear positional sensor which utilizes a pair of hollow, elongated sensing tubes constructed of a magnetically saturable material. At least one sense wire runs through each of the tubular sensing elements parallel to its elongated axis and a pair of oppositely poled magnets are positioned adjacent diametrically opposite surface portions of the sensing elements so that the magnetic flux from the magnets will substantially saturate the portion of the tubular sensing elements that lie therebetween, while the remaining portion of these sensing elements will remain relatively unsaturated. The positional sensor that is thus formed provides an extremely accurate linear indication of the position of the magnets with respect to the tubular sensing elements. Because the tubular sensing elements provide a closed flux path, there is no substantial fringing effect near the ends of the saturating magnets and, therefore, the portion of the sensing elements that are not between the magnets will remain substantially unsaturated. More specific details relating to the general type positional transducer that may be utilized in the improved sensor of the present invention is shown in Victor M. Bernin U.S. Pat. No. 3,958,203 issued May 18, 1976 to the assignee of the present invention, and this patent is herein incorporated by reference.
In the past, sensing elements of the described type were installed in their housings and adjusted to an initial position, whereupon they were then staked, or locked, into place. In the improved design of the present invention, a molded threaded stud for adjustment of the position of the plunger or control member is integrally formed as part of the end cap of the housing assembly. The housing has a flat on it which keeps it from rotating during adjustment and the sensor is mounted in a fixture during adjustment which should have a mating flat. An adjusting nut may then be screwed onto the stud to adjust the plunger or control member to their proper position. Once the desired position of the plunger or control member is reached, a lock nut, or lock tabs, may be used to keep the adjusting nut from turning.
The improved sensor is very easily assembled, since the elongated magnetically permeable tubular sensing elements are retained in place by two snap-together sections which form a relatively flat support plate for the elements. The two members of the support plate may be snapped onto an ultrasonically welded wire holding block which holds the interconnecting wire leads that connect the sensor to a remote connector. The interconnecting leads are relatively large wires, while the wires that thread the sensing elements are much smaller in diameter and run through a channel formed in the support plate for the elongated sensing elements for substantially most of their lengths. Only small portions of the wires that thread the sensing elements extend from the support plate and these are wrapped around and soldered to the bare end portions of the interconnecting wires which project through the wire holding block at substantially a right angle with respect to the elongated tubular sensing elements and the direction of orientation of the small sense wires that are threaded through the sensing elements.
The movable control member sub-assembly, which holds a pair of opposed permanent magnets has a central slot in it which receives the support plate for the sensing elements and thereby allows the magnets to be positioned directly over diametrically opposite portions of the tubular sensing elements. When the magnets are thus located, the movable control member sub-assembly is secured in place with respect to the support plate, and these two sub-assemblies may then be inserted together as a unit into the housing. The housing is provided with a pair of vertically oriented slots which receive and guide the support plate. The housing is also formed with a pair of horizontally disposed slots that are cut through two parallel, cylindrically shaped sections formed on the inner wall of the housing, each of which receives a wing that extends from the movable actuator of the control member sub-assembly, thereby guiding and positioning the control member sub-assembly with respect to the sensing elements. An elongated coil spring is inserted into each of these elongated cylindrical channels to provide a return bias for the control member sub-assembly. The sensor of the present invention, therefore, insures that the tubular sensing elements and the control magnets that are carried by the actuator are correctly positioned relative to each other at all times and, in addition, provides a structure that is easily assembled and adjusted.
The positional transducers of the present invention are very linear in response, are contactless, are very accurate and reliable and capable of functioning in severe environments and are in addition relatively low in cost. Moreover, the magnet force that is required to operate the device is not critical, because of the reliance on the saturation of the tubes between the magnets to produce the output signal.